1. Field of the Invention
The invention relates to an apparatus comprising at least one jetting section for levitational guidance and stabilization of a continuous web of material for the purpose of its heat-treatment, the apparatus comprising levitation nozzles for jetting the web at least on one side with a treatment gas and a radial fan arranged on the jetting side of the web including a 360.degree. spiral housing for feeding the levitation nozzles.
In such an apparatus the web is maintained levitated by being jetted with treatment gas from below, and also from above, where necessary, while being simultaneously heat-treated. Heat treatment may involve heating and maintaining the annealing temperature as well as subsequent cooling for metallurgical reasons or also for the purpose of surface treatment, e.g. in drying a web coating.
2. Description of the Prior Art
An apparatus of this kind is, as a rule, configured of individual sections in sequence, and as is evident from e.g. German disclosure DE-OS 2446983 or DE 4010280 A1, each section contains a form duct including at least one fan and systems of levitation nozzles arranged above and below the web transversely to the transport direction thereof with which the web is jetted with the gas circulated by the fan for the purpose of the convective heat exchange and at the same time is stabilized by the effective flow forces.
In particular, those apparatus for operation at high gas temperatures are generally equipped with radial fans to meet the technical strength requirements.
Although in the apparatus as disclosed by DE-OS 2446983 a particularly compact design is achieved by arranging only one fan at the side of each section, since one fan supplies top and bottom levitation nozzles at the same time, however, there is no possibility of simply regulating the supporting force, e.g. in adapting it to the weight of the web to be levitationally guided by changing fan speed, since this affects both the top and bottom nozzle systems in the same way. In addition to this the apparatus as disclosed by DE-OS 2446983 has the drawback that the return flow of the treatment gas jetted against the web occurs only on one side to the fan. This results in a heat exchange between the return flow from the web and the supply flow to the nozzles ribs, as a result of which a drop in temperature of the jetted gas occurs along the nozzle ribs from the side facing away from the fan to the side of the fan e.g. in a heating zone in which the down flow from the web is colder than the supply flow jetted to the web.
Although the apparatus as disclosed by DE 4010280 A1 obviates this disadvantage by alternating the supply flow to the nozzle ribs within a section, this requires four fans for each section and is thus suitable only for systems for levitationally guiding very wide webs where this added technical complexity is worthwhile due to the larger surface areas to be jetted and the thus higher gas flow rate required. One major drawback of this apparatus, having nozzle ribs supplied at the side, is that complicated systems of guide vanes need to be employed to return the jetted flow perpendicularly back to the surface of the web, which in addition to added costs also causes appreciable pressure losses. It is however especially in the case of systems for the treatment of non-ferrous webs of brass, copper, bronze, German silver and similar materials that the width of the web is limited due to the rolling width usually being considerably smaller than that of aluminium or steel webs, so that the apparatus as disclosed by DE 4010280 A1 is hardly suitable for levitational guidance of the majority of non-ferrous metal webs which are usually relatively heavy and narrow.